The use of a high-performance computer system connected to a less powerful client computer system via network hardware and software is well known. The high performance computer system, commonly known as a compute server, typically is used primarily to provide additional computational power to support the client system.
One earlier system for utilizing a computer server with a client system involves batch processing. Programs that run on a client system submit requests to the compute server for it to run computation intensive programs. The compute server executes the programs, and communicates the results back to the client system.
Unfortunately, in batch processing, communication between the client system and a compute server ordinarily is not transparent to a user because, for example, a client system and a compute server typically do not share common access to data sets. Therefore, in batch processing special commands ordinarily must be provided by a user to the client system to initiate batch processing on the compute server.
Consequently, context information required by the compute server to run a program in a batch processing environment generally must be provided to it by the client system prior to a run. User context information, for example, is information that enables, defines or restricts the capabilities of a user in a system. Examples of typical user context information include: location and contents of disk files and user environment variables such as the natural language of the user.
Another earlier system for using a compute server with a client system involves a remote procedure call (RPC) distributed application computer network. In using such a distributed application network, a program is segmented at the time of its development and is implemented in multiple pads, including a part that runs on the compute server and another part that runs on the client system. Ordinarily, subroutines that require the computational power of the compute server are built into the program part that is run on the compute server. Other subroutines and the main program part generally are run on the client system.
A remote procedure call (RPC) is a procedure call in which a called routine executes in a different address space and thread than the calling routine. An RPC ordinarily involves the passing of a message from one address space to another address space. RPCs can be made to a thread in the same computer system or in a remote computer system.
Typically, in a system using such distributed applications, the program part that runs on the client system uses the context of the client system, and the program part that runs on the compute server uses the context of the compute server. If client context information is required in the program part running on the compute server, then a program developer must code such client context into the program at the time of its development.
Unfortunately, since separate program parts run on the client system and the compute server, there often is a relatively high level of network traffic between the client and the server due to the need to transport parameters between program parts on a per call basis. Also, the client system and the compute server generally must run the same operating systems in order to ensure source and data level portability of a program.
Thus, there has been a need for a computer network in which the compute server interface is substantially transparent to the client system user and in which context information can be transparently transported on program request between the client and compute server systems.
Furthermore, there has been a need for such a method in which there is source and data level portability even when the client system and the compute server use different operating systems. The present invention meets these needs.
A callback is a nested RPC in which either a called thread or a helper thread makes an RPC callback to the calling thread. Typically, for example, when a called thread is invoked through an RPC, information that identifies the calling thread is stored in a call block in the address space of the called thread. The identifying information in the call block is used by the present invention to locate the calling thread during callbacks.
In accordance with the present invention, information can be stored in conjunction with a call block to indicate when a callback is in progress. It would be desirable to use the information stored in such call blocks to control the use of RPC callbacks, for example, to delay a callback to the calling thread until another callback by another thread has been completed.
For additional information regarding the state of the art regarding Remote Procedure Calls, reference may be made to "Implementing Remote Procedure Calls," by Andrew D. Birrell and Bruce Jay Nelson, ACM Transactions on Computer Systems, Vol. 2, No. 1, pp. 39-59, February 1984 (ACM 0734-2071/84/0200-0039).